Field screening of diverse Brassica germplasm identifies high level resistance against white leaf spot disease
N. GUNASINGHE (1), M. You (1), M. J. Barbetti (1). (1) The University of Western Australia, Perth, Australia
White leaf spot (WLS) is an important fungal disease of oilseed Brassicas in many countries including Australia. The causative agent <i>Pseudocercosporella capsellae</i> infects a range of wild and cultivated crucifers. In Australia, WLS became prevalent during a period associated with the development of commercial canola varieties against blackleg disease with single dominant gene-based resistance, highlighting a need to identify resistance sources. Diverse <i>Brassica</i> germplasm collections from Australia, India and China (200 genotypes), were tested in field trials conducted at two locations. After sequential inoculations with a mixed mycelial suspension of four isolates of <i>P. capsellae</i>, disease severity was assessed on a 1-10 scale and Area Under Disease Progress Curve (AUDPC) values were computed. Wide variation was observed in AUDPC values among genotypes, ranging from highly susceptible at value of 375 to completely immune at 0. When comparing <i>B. napus</i> and <i>B. juncea</i> genotypes tested, <i>B. juncea</i> from India and Australia were overall more susceptible. AUDPC values for vegetable Brassicas varied from 21 to 316 demonstrating wide variations in host resistance within the group. Twenty six genotypes from <i>B. carinata</i> (viz. 21 genotypes with AUDPC = 0 and 5 genotypes with AUDPC <5) showed high levels of resistance, indicating the tremendous potential to use such species in breeding programs for improvement of resistance in commercial <i>Brassica</i> crops against this pathogen.
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